Confined combustion of TNT explosion products in air

Description

Effects of turbulent combustion induced by explosion of a 0.8 kg cylindrical charge of TNT in a 17 m<sup>3</sup> chamber filled with air, are investigated. The detonation wave in the charge transforms the solid explosive (C<sub>7</sub>H<sub>5</sub>N<sub>3</sub>O<sub>6</sub>) to gaseous products, rich (~20% each) in carbon dust and carbon monoxide. The detonation pressure (~210 kb) thereby engendered causes the products to expand rapidly, driving a blast wave into the surrounding air. The interface between the products and air, being essentially unstable as a consequence of strong acceleration to which it is subjected within the blast wave, evolves into a turbulent mixing layer-a ...
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Description

Effects of turbulent combustion induced by explosion of a 0.8 kg cylindrical charge of TNT in a 17 m<sup>3</sup> chamber filled with air, are investigated. The detonation wave in the charge transforms the solid explosive (C<sub>7</sub>H<sub>5</sub>N<sub>3</sub>O<sub>6</sub>) to gaseous products, rich (~20% each) in carbon dust and carbon monoxide. The detonation pressure (~210 kb) thereby engendered causes the products to expand rapidly, driving a blast wave into the surrounding air. The interface between the products and air, being essentially unstable as a consequence of strong acceleration to which it is subjected within the blast wave, evolves into a turbulent mixing layer-a process enhanced by shock reflections from the walls. Under such circumstances rapid combustion takes place where the expanded detonation products play the role of fuel. Its dynamic effect is manifested by the experimental measurement of ~3 bar pressure increase in the chamber, in contrast to ~1bar attained by a corresponding TNT explosion in nitrogen. The experiments were modeled as a turbulent combustion in an unmixed system at infinite Reynolds, Peclet and DamkGhler numbers. The CFD solution was obtained by a high-order Godunov scheme using an AMR (Adaptive Mesh Refinement) to trace the turbulent mixing on the computational grid in as much detail as possible. The evolution of the mass fraction of fuel consumed by combustion thus determined exhibited the properties of an exponential decay following a sharp initiation. The results reveal all the dynamic features of the exothermic process of combustion controlled by fluid mechanic transport in a highly turbulent field, in contrast to those elucidated by the conventional reaction-diffusion model.